An object's spatially varying reflectance is a complex, 6D function, which can be represented by its spatially varying bidirectional reflectance distribution function. Realistic reflectance is critical for convincing computer graphic rendering. Previously, capturing “realistic reflectance” from real world targets required expensive hardware and slow scanning and processing.
For example, a gonioreflectometer is a device that directly measures the bidirectional reflectance distribution function at a single surface point by densely sampling the angular domain of light and view directions. A single camera and light source can be moved to capture reflectance at multiple positions or multiple cameras and light sources may be mounted over a spherical dome. Other solutions leverage a curved mirror or a condenser lens. Direct measurement data have been increasingly employed in recent rendering and editing works.
Image-based methods capture a single bidirectional reflectance distribution function from a homogeneous curved surface of known geometry by varying directional lighting. Non-directional lighting has also been applied.
Sparse views of a homogeneous sphere have been used to infer bidirectional reflectance distribution function and illumination.
Modeling an isotropic bidirectional reflectance distribution function as a general bivariate function of two angles (between normal and halfway vectors, and light and halfway vectors) can be employed to acquire a bidirectional reflectance distribution function from a single high dynamic range image of a homogeneous sphere and known environmental lighting captured by a light probe.
Most recently, statistical analysis of real-world illumination has been used to estimate a bidirectional reflectance distribution function from a single image of a homogeneous sphere under unknown lighting. Both reflectance and geometry of a homogeneous curved surface can be acquired by using a specialized coaxial optical scanner with spatially modulated light source.
These approaches all capture the bidirectional reflectance distribution function of a homogeneous surface of a target but cannot be easily extended to capture the bidirectional reflectance distribution function of a spatially varying surface of a target.